A cohort study of 3,400 subjects selected at random with precancerous gastric lesions in Shandong, China revealed a significantly elevated risk of gastric cancer for subjects with baseline superficial intestinal metaplasia (IM)(Odds Ratio (OR)=17.1), deep IM or mild dysplasia (DYS) (OR=29.3) and moderate or severe DYS (OR=104.2), as compared with subjects with chronic atrophic gastritis(CAG) at baseline. Helicobacter pylori (H. pylori) infection at baseline was a risk factor for progression to DYS/GC after a 4.5-year follow-up (OR=1.8, 95% CI, 1.2-2.6). The risks of the progression to DYS/GC increased with the number of years of smoking cigarettes and with number of cigarettes smoked. In contrast, risks of progression to DYS/GC decreased by 80% (OR=0.2, 95% CI, 0.1-0.7) among persons with 1989-1990 serum ascorbic acid levels in the highest tertile, as compared with those with lower levels. An endoscopic survey conducted among 214 adults aged 35-64 in Cangshan County, a low-risk area for gastric cancer in Shandong, confirmed the low prevalence of precancerous gastric lesions there and suggested that gastric lesions were strongly associated with H. pylori infection. The OR of CAG associated with H. pylori positivity was 4.2, while the OR of IM/DYS associated with H. pylori positivity was 31.5. Interestingly, this region is known for its production of garlic, which the inhabitants consume at a rate of 20 grams of garlic per day on average. The consumption of garlic showed non-significant protective effects and an inverse association with H. pylori infection. A study of H. pylori infection and mode of transmission among 98 children aged 3-12 years and 289 adults aged 35-64 in Linqu County showed that the prevalence of H. pylori infection clustered within families with at least one infected parent (OR=30.4). A recent study found no evidence to suggest that exposure to pets or other domestic animals during either childhood or adulthood was related to the prevalence of H. pylori infection.